Metacat

/**

 *        Name: MetaCatServlet.java

 *     Purpose: A Class that implements a metadata catalog as a java Servlet

 *   Copyright: 2000 Regents of the University of California and the

 *              National Center for Ecological Analysis and Synthesis

 *     Authors: Matt Jones

 * 

 *     Version: '$Id: MetaCatServlet.java 51 2000-04-17 23:06:07Z jones $'

 */

package edu.ucsb.nceas.metacat;

import java.io.PrintWriter;

import java.io.IOException;

import java.io.Reader;

import java.io.StringReader;

import java.util.Enumeration;

import java.util.Hashtable;

import java.net.URL;

import java.net.MalformedURLException;

import java.sql.Connection;

import javax.servlet.ServletConfig;

import javax.servlet.ServletContext;

import javax.servlet.ServletException;

import javax.servlet.ServletInputStream;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import javax.servlet.http.HttpUtils;

import oracle.xml.parser.v2.XSLStylesheet;

import oracle.xml.parser.v2.XSLException;

import oracle.xml.parser.v2.XMLDocumentFragment;

import oracle.xml.parser.v2.XSLProcessor;

/**

 * A metadata catalog server implemented as a Java Servlet

   *

   * <p>Valid parameters are:<br>

   * action=query -- query the values of all elements and attributes

   *                     and return a result set of nodes<br>

   * action=getdocument -- display an XML document in XML or HTML<br>

   * qformat=xml -- display resultset from query in XML<br>

   * qformat=html -- display resultset from query in HTML<br>

   * action=getdocument -- display an XML document in XML or HTML<br>

   * docid=34 -- display the document with the document ID number 34<br>

 */

public class MetaCatServlet extends HttpServlet {

  private ServletConfig		config = null;

  private ServletContext	context = null;

  DBSimpleQuery		queryobj = null;

  DBReader		docreader = null;

  static  String 	user = MetaCatUtil.user;

  static  String 	password = MetaCatUtil.password;

  static  String 	defaultDB = MetaCatUtil.defaultDB;

  static  String 	resultStyleURL = "file:///home/httpd/html/xmltodb/resultset.xsl";

  /**

   * Initialize the servlet by creating appropriate database connections

   */

  public void init( ServletConfig config ) throws ServletException {

    try {

      super.init( config );

      this.config = config;

      this.context = config.getServletContext();

      try {

        // Open a connection to the database

        Connection dbconn = MetaCatUtil.openDBConnection(

                "oracle.jdbc.driver.OracleDriver",

                defaultDB, user, password);

        queryobj = new DBSimpleQuery(dbconn);

        docreader = new DBReader(dbconn);

      } catch (Exception e) {

      }

    } catch ( ServletException ex ) {

      throw ex;

    }

  }

  /** Handle "GET" method requests from HTTP clients */

  public void doGet (HttpServletRequest request, HttpServletResponse response)

    throws ServletException, IOException {

    // Get the parameters from the form

    String querystring = request.getQueryString();

    Hashtable params = HttpUtils.parseQueryString(querystring);

    // Process the data and send back the response

    handleGetOrPost(response, params);

  }

  /** Handle "POST" method requests from HTTP clients */

  public void doPost( HttpServletRequest request, HttpServletResponse response)

    throws ServletException, IOException {

    // Get the input data from the client

    ServletInputStream in = request.getInputStream();

    int len = request.getContentLength();

    // Parse the input data into a Hashtable

    Hashtable params = HttpUtils.parsePostData(len, in);

    // Process the data and send back the response

    handleGetOrPost(response, params);

  }

  /**

   * Control servlet response depending on the action parameter specified

   */

  private void handleGetOrPost(HttpServletResponse response, Hashtable params) 

    throws ServletException, IOException {

    // Get a handle to the output stream back to the client

    PrintWriter out = response.getWriter();

    String action = ((String[])params.get("action"))[0];

    if (action.equals("query")) {

      handleQueryAction(out, params, response);

    } else if (action.equals("getdocument")) {

      handleGetDocumentAction(out, params, response);

    } else {

      out.println("Error: action not registered.  Please report this error.");

    }

    // Close the stream to the client

    out.close();

  }

  /** 

   * Handle the database query request and return a result set, possibly

   * transformed from XML into HTML

   */

  private void handleQueryAction(PrintWriter out, Hashtable params, 

               HttpServletResponse response) {

      // Run the query

      String query = ((String[])params.get("query"))[0]; 

      Hashtable nodelist = queryobj.findRootNodes(query);

      // Create a buffer to hold the xml result

      StringBuffer resultset = new StringBuffer();

      // Print the resulting root nodes

      long nodeid;

      resultset.append("<?xml version=\"1.0\"?>\n");

      resultset.append("<resultset>\n");

      resultset.append("  <query>" + query + "</query>");

      Enumeration rootlist = nodelist.keys(); 

      while (rootlist.hasMoreElements()) {

        nodeid = ((Long)rootlist.nextElement()).longValue();

        resultset.append("  <nodeid>" + nodeid + "</nodeid>");

      }

      resultset.append("</resultset>");

      String qformat = ((String[])params.get("qformat"))[0]; 

      if (qformat.equals("xml")) {

        // set content type and other response header fields first

        response.setContentType("text/xml");

        out.println(resultset.toString());

      } else if (qformat.equals("html")) {

        // set content type and other response header fields first

        response.setContentType("text/html");

        //out.println("Converting to HTML...");

        XMLDocumentFragment htmldoc = null;

        try {

          XSLStylesheet style = new XSLStylesheet(new URL(resultStyleURL), null);

          htmldoc = (new XSLProcessor()).processXSL(style, 

                     (Reader)(new StringReader(resultset.toString())),null);

          htmldoc.print(out);

        } catch (Exception e) {

          out.println("Error transforming document:\n" + e.getMessage());

        }

      }

  }

  /** 

   * Handle the database getdocument request and return a XML document, 

   * possibly transformed from XML into HTML

   */

  private void handleGetDocumentAction(PrintWriter out, Hashtable params, 

               HttpServletResponse response) {

      // Get the document indicated

      String docid = ((String[])params.get("docid"))[0]; 

      String doc = docreader.readXMLDocument((new Long(docid)).longValue());

      // set content type and other response header fields first

      response.setContentType("text/xml");

      out.println(doc);

  }

}